The invention relates to a magnetoresistive transducer and to a method for the manufacture of such a transducer.
The transfer of electrons in Magnetic Metal Multilayers has been studied for the past few years because it enables the study of the magnetoresistance of a material considered. This phenomenon originates in the difference in resistivity of the material, under an external magnetic field, or in the absence of this field, related to the variation of the properties of the interfaces.
In FIG. 1a, a type A material for example is magnetic while a type B material is non-magnetic.
For practical reasons, the measurements are generally made only by applying an electrical field in parallel to the planes of the layers. In this case, if the diffusion length (5 to 100 nm) is greater than the thickness of the layers (1 to 5 nm), the path taken by an electron before it meets an interface may be great. The approach wherein an electrical field is applied perpendicularly to the planes of the layers (FIG. 1b) would therefore be far more favorable for the use of magnetoresistance with higher efficiency since, in this case, the electrons would swiftly encounter an interface. This idea has therefore been circulating for some years, but it is very difficult to achieve technically, and the object of the invention lies in an approach that circumvents these difficulties.
Practical embodiments that work by the measurement of the current perpendicularly to the plane of the layers may take the form shown in FIG. 1c.
It can then be noted that:
1.degree./ Since the resistivity of the materials is low (about 10.sup.-5 .OMEGA..cm), the values of resistance to be measured are very low. PA1 3.degree./ The technology is little-known and difficult. PA1 4.degree./ The currents to be measured are low for it is not possible to let through a great deal of current (in comparison with electron transfer parallel to the layers). PA1 5.degree./ It is difficult, with conventionally envisaged approaches, to place an object having a magnetic information element close to the detection device (the making of contacts means that the medium containing the information cannot be placed in the vicinity). PA1 two layers of conductive material enclosing the layer of composite material; PA1 at least two electrodes located on at least one of the layers of conductive materials in zones that are distant from each other along the plane of the layers; the layer of composite material and a layer of conductive material that bears an electrode comprising at least one interruption of electrical conduction located between the zones comprising the electrodes. PA1 a) the making of a stack of at least the following layers: PA1 b) the making of at least one interruption of electrical conduction in one of the layers of conductive material and in the layer of composite material.
For example: ##EQU1## 2.degree./ The contact resistance R.sub.c is in a high proportion for the contact surface area is small (some .mu.m.sup.2).
Because of these reasons, no coherent studies under ambient temperature have been made to date, and measurements have been made only at low temperatures by using superconductive connections which, of course, limit the observations solely to the field of low temperatures. Hence, at present, there are no plans to make sensors that have the advantage of perpendicular electron transfer and work at ambient temperature.